This application is based on the patent application No. 11-316830 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an actuator utilizing a piezoelectric transducer that is formed in a cylindrical shape by coiling sheet type piezoelectric elements.
2. Prior Art
An actuator utilizing a piezoelectric transducer assures high conversion efficiency for converting electric energy supplied to a drive force, large drive force to be generated although small size and light weight and easier control of drive force. Therefore, this actuator has been used for drive and positioning of the members to be driven of a camera, a measuring instrument and the other high precision apparatuses.
A piezoelectric transducer formed as a drive source to be used in such actuator is formed, for example, by laminating a plurality of sheets of unit piezoelectric element because it is requested to obtain a large displacement as possible in the thickness direction generated in a unit piezoelectric element.
A piezoelectric transducer formed by laminating a plurality of sheets of the unit piezoelectric element has been obtained at a higher cost because it is manufactured through complicated processes including the process to provide an electrode on the surface of unit element, the process to laminate and bond the sheets of piezoelectric element and the process to connect the electrode of each layer.
Therefore, there is proposed a piezoelectric transducer that has been formed by winding, in the hollow cylindrical form, a laminated material that has been formed by laminating two sheets of thin plate type piezoelectric elements having formed an electrode as its surface.
FIG. 16 is a perspective view illustrating an example of a piezoelectric transducer that is formed in the cylindrical shape by laminating such two sheets of thin plate type piezoelectric elements. FIGS. 17(a) and 17(b) are diagrams for explaining the electrode forming surface and laminating condition. FIG. 18 is a plan view for explaining the condition of the end surface in the cylinder axis direction of the piezoelectric transducer formed cylindrically.
The manufacturing process of a piezoelectric transducer will be explained. First, as illustrated in FIG. 17(a), a first piezoelectric element 101 and a second piezoelectric element 102 formed of piezoelectric ceramics formed like thin plates are prepared. Here, the length in the winding direction of the second piezoelectric element 102 is set longer by the sized than the first piezoelectric element 101.
At the front surface of the first piezoelectric element 101, a first electrode 103 is formed while the rear surface is formed as an electrode non-forming surface. Moreover, at the front surface of the second piezoelectric element 102, a second electrode 104 is formed, while the rear surface is formed as the electrode non-forming surface (refer to FIG. 17(a)) Next, as illustrated in FIG. 17(b), the electrode non-forming surface of the first piezoelectric element 101 and the electrode forming surface of the second piezoelectric element 102 are laminated with these surfaces provided opposed with each other and this laminated material is then wound into a cylindrical shape as illustrated in FIG. 16 using a winding shaft for the working use formed of cellulose or the like. Thereafter, this cylindrical shape is baked in the predetermined temperature and then polarized, thereby burning and completing the piezoelectric transducer. Since the winding shaft for the working use is burned out with the baking process, a cylindrical space is left at the innermost part of the cylindrical material.
Since the length of the first piezoelectric element 101 in the winding direction is set shorter than the length of the second piezoelectric element 102 in the winding direction, when the cylindrical shape is formed, the end portions of first electrode 103 and the second electrode 104 exposed at the external circumference of the cylindrical shape are deviated and thereby these electrodes may be connected easily with the lead wires 103a and 104a. 
In the cylindrical piezoelectric transducer of the structure explained above, since the length of the first piezoelectric element 101 in the winding direction is set shorter than the length of the second piezoelectric element 102 in the winding direction, the end portions of the first electrode 103 and second electrode 104 are deviated when the cylindrical shape is formed. Therefore, these electrodes can easily be connected with the lead wires. But, Since the lead wire is extended from the external circumference part of the piezoelectric transducer, there rise disadvantages that the external size of the piezoelectric transducer as a whole becomes large and as a result, a wider space is required. The present invention has an object to solve such disadvantages.
The principal object of the present invention is to provide an actuator utilizing a piezoelectric transducer of a novel structure that is designed in small size as the entire part by introducing a newly applied power feeding terminals.
It is another object of the present invention to provide an actuator utilizing a piezoelectric transducer that is fed from the electrode exposed at the internal surface of cylindrical shape of the cylindrical piezoelectric transducer.
It is still another object of the present invention to provide an actuator utilizing a piezoelectric transducer of a novel structure wherein a sheet type piezoelectric element arranging the electrodes at both surfaces thereof is formed in the cylindrical shape and the power feeding terminals are placed in contact with the electrodes exposed as the internal surface of the cylindrical shape.
Other objects of the present invention will become apparent from detail explanation of the present invention with reference to the accompanying drawings.